It is known from European Application EP 0 785 605 A1 to provide ignition voltage for a spark plug in an internal combustion engine by use of a high voltage step-up transformer mounted directly above the spark plug. The high voltage transformer utilizes a magnetic core having a pencil-shape, and thus has become commonly known as a "pencil core".
FIGS. 1A, 1B, and 1C show an illustration of such a known prior art pencil core. As generally illustrated at 10 in the cross-sectional view of FIG. 1A, a plurality of thin magnetic metal laminations 11 of varying width, but having a substantially constant thickness and a same length are stacked so that a resulting substantially circular profile shown in FIG. 1B results.
In order to maintain the stack as a unified body, it is known to provide a plurality of rectangular embossments such as 12A, 12B, and 12C in each lamination 11 so that as shown in FIG. 1A or 1B, the embossment of the upper lamination fits into the inside of the embossment of the following lamination and so on until the last lamination at the bottom of the stack such as 13, where apertures 14A, B, C are provided in lieu of the embossments so that the next to the last lamination embossments fit within the apertures 14A, B, C, in the bottom lamination so that there is no projection beyond the bottom surface of the bottom lamination.
FIG. 1C shows a plan view clearly illustrating what the prior art pencil core looks like from the top viewing down upon the top most lamination. In FIG. 1C and also FIG. 1B it can be readily seen that the central two laminations of a total of twenty laminations 11, for example, have the same width, whereas laminations above and below the two central laminations have decreasing width.
It is known that such pencil core laminations, instead of rectangular embossments, can be held together such as by welding.